In an installation of this kind, an air filter is usually provided to filter the air passing into the installation. The filtered air is then treated and distributed into the passenger compartment by means of one or more nozzles disposed in selected positions in the passenger compartment.
Progressively during use of the installation the filter becomes dirty, causing it to become fouled and causing pressure losses prejudicial to the proper operation of the installation. Moreover, the fouling is often a source of disagreeable smells emitted into the passenger compartment when the installation is in operation. It is also possible that the filter may deteriorate with time and become torn or holed.
Usually the filter is contained in a replaceable cartridge which can be exchanged for a new cartridge when the filter is blocked, saturated or has deteriorated. For this purpose it is generally necessary for the operator to gain access to the installation, either in the engine compartment or in the passenger compartment, then to open an access flap and remove the cartridge to determine its condition, usually by a simple visual examination.
Because the filter is often placed in a position which is difficult to get to, these operation required tome and may prove useless if the operator decides, after examination of the filter, that the latter is still in good condition and therefore does not need to be exchanged.
The invention aims to avoid the above-mentioned disadvantages.
In particular, it is one object of the invention to provide means making it possible to determine the state of an air filter in an installation of the above kind, without it being necessary to dismount the filter.